A suicide bomber killed at least 15 people and wounded 90 on Friday in a Sunni Muslim mosque in northern Iraq whose imam had criticized al Qaeda, officials said, Reuters reported.

Police said the bomber attacked the mosque in Tal Afar in Nineveh province, 420 km (260 miles) northwest of Baghdad, during Friday prayers. An official said the attacker shot dead a local judge praying there before detonating the explosives.

Suicide attacks are the hallmark of Sunni Islamist groups and it is rare for them to target Sunni rather than Shi'ite places of worship. The Tal Afar mosque was probably attacked because its imam had spoken out against al Qaeda and also to kill the judge, the official said.

Witness Qassim Ahmed, wounded by flying glass, told Reuters from hospital: "I came to the mosque late and when I went to enter, I heard shooting. Seconds later, a big explosion happened." Nineveh is seen as the last major holdout of insurgents who have been largely driven out of Baghdad and western Anbar province by Sunni tribal sheikhs allied to U.S. forces.

Tal Afar, mainly home to minority Turkmen Shi'ites, has been hit by many bombings, including two on July 9 that killed at least 34 people and one of Iraq's deadliest, which killed 152 in March 2007.

Iraq has seen a dramatic fall in attacks over the last 18 months and the sectarian carnage that gripped the country a few years ago has largely ended.

Still, bombings, shootings and other killings occur daily and are expected to increase ahead of a general election in the world's 11th largest oil producer in January.